1. Field of the Invention
This invention relates to a method of making solar cells from silicon spheres disposed in a metal foil matrix wherein the cells generate electricity upon exposure to light.
2. Description of the Prior Art
Systems for producing energy by conversion of the rays of the sun to other forms of useful energy are well known and such devices are constantly being developed and improved due to the economics of the sun being the primary source of energy involved. One such system is disclosed in U.S. Pat. No. 4,021,323 of Kilby et al. wherein a solar array composed of a transparent matrix such as glass or plastic is provided with particles of silicon of P-type with an N-type skin on one side thereof or N-type with a P-type skin on one side thereof embedded in the matrix. Preferably about half of the particles are P-type with N-type skin and the remainder are N-type with a P-type skin though this arrangement can be altered. On the backside of the matrix, the silicon particles protruding therethrough are interconnected by appropriate electrically conductive metallization. The silicon particles have the skin portion thereof extending through the frontside of the matrix. These arrays are immersed in an electrolyte, preferably hydrobromic acid (HBr), that contacts the frontside of the matrix. Due to the potential difference between the silicon particles of different conductivity type contacting the electrolyte, a potential difference therebetween is set up under sunlight which electrolyzes the HBr into hydrogen gas which bubbles off and bromine which remains in solution. The hydrogen gas is collected and is a source of energy, for example, in fuel cells and the like as is well known.
In solar arrays of this type, the silicon particles participate in the electrolysis independently. As a result, the rate at which reaction products are generated by an array will not be significantly affected if the P-N junctions in a few particles are shorted or shunted.
Another system for producing useful energy from the sun's rays uses an array similar to the kind described above but configured so as to generate electricity rather than perform electrolysis. One such system is disclosed in U.S. Pat. No. 2,904,613. Although alternate arrangements are possible, a useful embodiment comprises a transparent matrix such as glass or plastic provided with particles of N-type silicon with a P-type skin. The N-type cores of the particles protrude through the backside of the matrix and are interconnected by appropriate electrically conductive metallization. The P-type skins protrude through the frontside of the matrix and are interconnected with an electrically conductive light transmissive material such as tin oxide on a fine metal gridwork. Under sunlight, a potential difference is set up between the backside and frontside interconnections of such an array which can be suitably connected so as to power an external electrical load directly.
An improvement over this prior art is set forth in the application of Kent R. Carson, Ser. No. 562,782, filed Dec. 15, 1983 (TI-9744), wherein refinements and improvements to the above noted inventions were made. However, in the present state of the art, the cost of producing solar arrays in accordance with the above described prior art is relatively uneconomical and this prior art approach has not shown a great measure of economic success to date. It is therefore imperative, in order to provide economically viable solar arrays, that such arrays be capable of relatively inexpensive fabrication.